1.) Studies with mammalian cytochrome aa3 (cox): Our SVD-analyzed multichannel study of the kinetics of electron transfer events in the oxidation of fully reduced cox by O2 revealed four steps with time constants tau of 0.01, 0.09, 1.1, and 30 ms. When analyzed according to the traditional linear sequence model, no evidence was found for the suspected oxyferryl (Fe4+) intermediate. A mathematical approach was developed to allow analysis of the data in terms of a branched model that is indicated by cryogenic EPR studies. This analysis fully supported the EPR and resonance Raman studies implicating the oxyferryl intermediate. It substantiates the branched model at room temperature and points to CuB as a stronger O2-anchor site than Fe2+. 2.) Studies with bacteriorhodopsin (BR): Conditions for optimal reconstitution of the bacteriorhodopsin (BR) photocycle in Triton-treated purple membranes (PM) were defined. It was shown that the ability of lipids to repair the damage to the structure, function, and regulation of the BR photocycle is specific; PM lipids are more effective than foreign lipids and certain particular combinations of PM lipids are more effective than others. The requirement for salt in the lipid- reconstitution process is shown to involve both Gouy-Chapman screening of surface charges and specific binding of cations. One of the major surface charges is a proton-binding group with pKapp of 5, which is more likely due to an acidic amino acid than a lipid phosphate group (pK about 1-2). Agents which alter viscosity and water activity profoundly affect the kinetics and pathway of the BR photocycle. Experiments to distinguish the viscosity from the water activity effects have been started.